Physiological and subjective responses to low relative humidity

Sunwoo Y, Chou C, Takeshita J, Murakami M, Tochihara Y.

Abstract

The study was designed to investigate the subjective and physiological responses of young and old males exposed to different humidity levels (10, 30 and 50%) for 120 minutes in a climatic chamber. The study was done in two parts.

1 - Experiment exposed 16 young and healthy Japanese males and measured the following parameters:

Velocity of “Mucociliary Clearance” by Saccharin Clearance Time, before and after exposure

2 - Experiment compared groups of young (8, Ø 22y.) and old men (8, Ø 71y.)

The pre-room conditions were maintained at 25 °C and a relative humidity (RH) of 50%. Subjects were sitting in the climatic chamber with light clothes (T-shirt) and without physical activities.

Results

Saccharin Clearance time increased in low humidity and was significantly increased in 10% compared to 50%RH.

Saccharin Clearance time in low humidity was significantly higher in old than in young men.

TEWL increased with lower humidity. The mean total weight loss in 120 min. exposure was 230gr (10%RH), 200gr (30%RH), 180ml (50%RH). This corresponds to an insensible fluid loss of 115, 100 and 90 ml/h in 10, 30 and 50%RH.

Blinking Frequency increased significantly in 10% compared to 50%RH.

Young persons had a better perception of dryness in throat and eyes, but dryness wasn’t felt on the body skin. All subjects could feel dryness after 90 minutes but comfort feeling didn’t change in different humidity’s.

The increased TEWL in the first minutes of low humidity exposure was felt as lowered room temperature because of the evaporative cooling effect. The mean body skin temperature fell significantly lower (-0,6 °C) in older men due to higher evaporative fluid loss.

The study provides evidence for a drying effect of low humidity on our eyes, skin and mucous membranes. The effect of decreased mucociliary clearance (↑Saccharin Clearance Time) is more prominent in older men, but is perceived less accurately than by young men.

Exposure to low humidity environments has an impact on our fluid balance. It increases insensible fluid loss significantly in the first two hours of exposure without physical activity. Building occupants should be guided to increase fluid intake in heated, dry environments.

Moreover, the study confirms once again, that lower humidity environments are perceived as cooler. Although subjects couldn't feel the change in humidity on their skin (but in nose and throat!), they sensed a drop of temperature, when humidity decreased.

For the building service industry, this means that maintaining a higher humidity reduces the building's heating requirements by around 2°C. This represent an energy saving of around 10% of the total energy consumption for heating.